1. Field of the Invention
This invention relates to a camera system, and in particular concerns infrared (IR) camera systems which may be used in environments where the ambient temperature is likely to fluctuate rapidly.
2. Prior Technology
Fluctuations in temperature raise problems for imaging devices, in particular IR imaging devices, and if temperature gradients exist within the optical systems and the sensor of an IR camera, this can lead to significant deterioration of the image produced by the camera.
Some modern motor vehicles include an IR camera which is located under the bonnet of the vehicle, with the field of view of the camera pointing forwardly of the vehicle. Normally the camera is used to display an image of the scenery in front of the driver. This image will help the driver to see, particularly in the case of relatively warm objects (such as pedestrians), in dark conditions. The image from the camera could also be processed to identify and mark objects that should be observed by the driver. Clearly, accurate readings are needed from the IR camera for such a system to function effectively.
The ambient temperature under the bonnet of a motor vehicle is, however, liable to fluctuate significantly during the course of a journey. For instance, when the vehicle is idling the temperature under the bonnet may reach 60° C. When driving at a moderate speed, however, the temperature under the bonnet may drop to that of the ambient air (e.g. 20° C.).
Many IR cameras include a processing arrangement, which will generally comprise one or more integrated circuits, and this processing arrangement may generate a significant quantity of heat. To counter this, it is common to provide a heatsink which is in thermal contact with the processing arrangement, and which conducts heat energy from the processing arrangement to the surroundings of the camera.
It will be appreciated, however, that when the temperature of the camera surroundings reaches a high level, for instance when the vehicle is idling, the heatsink will then conduct heat energy from the surroundings into the camera.
These effects are likely to cause temperature gradients within and around the optical systems and the sensor of the camera, as well as raising and lowering the overall temperature of the optical systems and the sensor rapidly. It will be appreciated that this will tend to deteriorate the quality of the images that are captured by the camera.
The manner in which heat is generated within, or transferred to, the camera system may lead to constant and predictable thermal gradients within the camera system. Such constant gradients, however, can be accommodated by making systematic adjustments, for example by incorporating a consistent weighting into the way in which the signals from the camera system are interpreted. However, more random, unpredictable gradients and overall changes in temperature cannot be accommodated in the same way.
It is an object of the present invention to seek to ameliorate one or more of the above problems.